Present and future environmental impact of the Chernobyl accident

Transcription

1 IAEA-TECDOC-1240 Present and future environmental impact of the Chernobyl accident Study monitored by an International Advisory Committee under the project management of the Institut de protection et de sûreté nucléaire (IPSN), France August 2001

2 The originating Section of this publication in the IAEA was: Waste Safety Section International Atomic Energy Agency Wagramer Strasse 5 P.O. Box 100 A-1400 Vienna, Austria PRESENT AND FUTURE ENVIRONMENTAL IMPACT OF THE CHERNOBYL ACCIDENT IAEA, VIENNA, 2001 IAEA-TECDOC-1240 ISSN IAEA, 2001 Printed by the IAEA in Austria August 2001

3 FOREWORD The environmental impact of the Chernobyl nuclear power plant accident has been extensively investigated by scientists in the countries affected and by international organizations. Assessment of the environmental contamination and the resulting radiation exposure of the population was an important part of the International Chernobyl Project in This project was designed to assess the measures that the then USSR Government had taken to enable people to live safely in contaminated areas, and to evaluate the measures taken to safeguard human health there. It was organized by the IAEA under the auspices of an International Advisory Committee with the participation of the Commission of the European Communities (CEC), the Food and Agriculture Organization of the United Nations (FAO), the International Labour Organisation (ILO), the United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR), the World Health Organization (WHO) and the World Meteorological Organization (WMO). The IAEA has also been engaged in further studies in this area through projects such as the one on validation of environmental model predictions (VAMP) and through its technical co-operation programme. The project described in this report was initiated after a proposal by Belarus to the 38th regular session of the IAEA General Conference in September 1994 to convene an international group of high level experts to review the information drawn from the long term studies of the Chernobyl accident and its consequences. After other relevant international organizations had been consulted, it was agreed that the IAEA would formulate a project focusing on the environmental impact of the Chernobyl accident. France responded favourably to the IAEA's invitation to help finance this study, supporting it through the Institut de protection et de sûreté nucléaire (IPSN). The IPSN provided the head of the project, D. Robeau, assisted by a group of technical advisers. The technical investigation of the material reviewed and the drafting of the working document necessary for the compilation of the final report were carried out by specialists in fields including radioecology, radiation protection, rehabilitation and recovery, economics and sociology from Belarus, the Russian Federation and Ukraine. The work was based on the national reports and additional material including experimental data obtained and analysed by experts from these three States by The work was supervised by a project supervisory committee made up of senior experts nominated by the Governments of Belarus, the Russian Federation and Ukraine, one expert from France and a chairman, P. Hedemann Jensen, from Denmark. This committee approved the final report after considering comments from five renowned experts who formed an international peer review committee. "We propose that the IAEA, UNESCO, the World Health Organization and other interested organizations together with the scientists and specialists from Russia, Ukraine and Belarus will analyze and generalize the results of ten years study of the Chernobyl accident. For this reason it seems advisable to form an international group of high-level experts. There is no such necessity at all for this group, as a rule, to go to the contaminated areas and carry out the investigations there. Its task is to study and generalize the material having been already accumulated. In this case the Republic of Belarus is ready to present all the necessary materials. The result of such a work could be the publication of a special final report." (Taken from the Statement of the Head of the Delegation of the Republic of Belarus Mr. A. Mikhalevich at the XXXVIII Session of the IAEA General Conference, 1994).

4 The project had to be completed within a very short time. Its successful completion was only possible with a substantial contribution from the IPSN and the commitment shown in Belarus, the Russian Federation and Ukraine. These and other contributors, listed at the end of the report, are gratefully acknowledged. A draft of this report was originally during the EC/IAEA/WHO International Conference, "One Decade after Chernobyl: Summing up the Consequences of the Accident", held in Vienna, 8 12 April Comments of the Peer Review Committee and of others have been taken into account in the final version of the report. The efforts of P.J. Waight in unifying the terminology and ensuring clarity of expression are gratefully acknowledged. The IAEA officers responsible for this publication were M. Balonov and M. Gustafsson of the Division of Radiation and Waste Safety. EDITORIAL NOTE The use of particular designations of countries or territories does not imply any judgement by the publisher, the IAEA, as to the legal status of such countries or territories, of their authorities and institutions or of the delimitation of their boundaries. The mention of names of specific companies or products (whether or not indicated as registered) does not imply any intention to infringe proprietary rights, nor should it be construed as an endorsement or recommendation on the part of the IAEA.

5 CONTENTS SUMMARY INTRODUCTION Background Objective and scope Structure CURRENT RADIOLOGICAL SITUATION AND PROGNOSIS FOR THE FUTURE Soil contamination with radionuclides Release of radionuclides and contamination of territories Vertical migration of radionuclides in the soil Radioactive contamination of water bodies Radioactive contamination affecting agriculture Soil-to-plant transfer Levels of contamination in agricultural products Radioactive contamination of forest Tree contamination Contamination of mushrooms and berries Individual annual doses and lifetime doses to the population Doses to the thyroid External dose Internal dose from long lived radionuclides Dose rate reduction with time...33 References to Section FACTORS AFFECTING LIFE IN THE CONTAMINATED REGIONS Features common to the Commonwealth of Independent States (CIS) Effects on the well-being of the population Effects on industrial and agricultural production Changes in agricultural practices in the contaminated areas Conditions for safe living Situation in Belarus Effects on the well-being of the population Effects on industrial and agricultural production Changes in agricultural practices in the contaminated areas Conditions for safe living Perspectives for the future Situation in the Russian Federation Effects on the well-being of the population Effects on industrial and agricultural production Changes in agricultural practices in the contaminated areas Conditions for safe living Perspectives for the future...53

6 3.4. Situation in Ukraine Effects on the well-being of the population Effects on industrial and agricultural production Changes in agricultural practices in the contaminated areas Conditions for safe living Perspectives for the future References to Section RADIOBIOLOGICAL CONSEQUENCES OF IRRADIATION OF FLORA AND FAUNA IN THE EXCLUSION ZONE General radiological conditions Effects of radiation on the environment Impact of radiation on flora in the early phase of the accident Radiation damage to coniferous forest Restorative processes in perennial plants growing in the exclusion zone Mutagenic effects Impact of radiation on fauna Radiosensitivity of animals Changes in the microbiological composition of soil and water Prognosis for the ecological situation for the next 10 years Contamination by the resuspension of particles Contamination of forests Animals Contamination of soils Surface and underground water contamination References to Section REMEDIAL ACTIONS TO REDUCE LONG TERM EXPOSURE Criteria for intervention in the USSR ( ) and in Belarus, the Russian Federation and Ukraine ( ) Comparison of CIS criteria with international criteria Present international guidance CIS guidance versus present international guidance Effectiveness of the completed protection and rehabilitation measures and prospects for their future use Evacuation and resettlement Decontamination of land, buildings and installations Burial of radioactive waste Limits on free access by the population and the termination of economic activity Changes in agricultural and forestry activities Limitation of consumption of contaminated food products and drinking water Countermeasures in agriculture Measures for the reduction of contamination of food produced on private land plots Measures to improve populated areas... 99

7 Information to the population Social and other supplemental measures References to Section CONCLUSIONS Radiological impact Radionuclide release and deposition Radionuclide migration Present and future human exposure Factors affecting life in the contaminated regions Effects on well-being Effects on industrial and agricultural production Conditions for safe living Impact on fauna and flora in the exclusion zone Radiological conditions Effects of radiation on biota Prognosis for the next ten years Remedial actions to reduce long term exposure Criteria for intervention in the CIS Effectiveness of the completed countermeasures Perspectives for the future ANNEX I: AREAS AND ZONES DISCUSSED IN THE REPORT ANNEX II: INTERNATIONAL CRITERIA FOR LONG TERM COUNTERMEASURES AS FOR CONTRIBUTORS TO DRAFTING AND REVIEW...127

8 .

9 SUMMARY This report presents the results of studies of the radiological and social consequences of the Chernobyl accident. The studies, carried out by experts from Belarus, the Russian Federation and Ukraine during the period , covered the current and likely radiological situation; the effects of the accident on human life in the contaminated regions; radiobiological consequences of the irradiation of flora and fauna in the exclusion zone; and remedial actions to reduce long term human exposure. The radiological data include recent estimates of the radionuclide releases in April May 1986 from the damaged reactor and of soil contamination levels in Belarus, the Russian Federation and Ukraine. It is shown that most of the long lived radionuclide activity is still concentrated in the upper (0 10 cm) soil layer. The report describes the dynamics of radionuclide concentration in surface water, in agricultural produce of vegetable and animal origin, in forest litter/soil and trees, and in mushrooms consumed by the local population. The results of reconstructions of the external and internal doses received by inhabitants of contaminated areas during the period and dose forecasts for are presented. For most of the population, external irradiation due to 137 Cs will be the main contributor to the total future dose. The report discusses the social and economic impact of the Chernobyl accident on the well-being of the people in the affected countries caused by reduced collective and private production and by trade restrictions due to the radioactive contamination of produce. Increased morbidity has been reported, attributable especially to thyroid cancer in children. The psychological state of people is characterized by high anxiety; the demographic situation is worsening because of the departure of young families. Radiation protection, medical services and economic aid are being provided and the affected areas are being rehabilitated through State programmes. The conditions of exposure of and the radiobiological effects on flora and fauna in the near exclusion zone are described. Here, the doses reached 100 Gy, killing and damaging conifers, suppressing the reproductive ability of plants and animals, and causing molecular and cellular abnormalities in wild and domestic animals. A forecast of ecological changes in the exclusion zone is given for the next decade. The report pays special attention to the experience of applying radiation protection measures in the post-accident period. Also, it presents the history of implementation of countermeasures at different stages: evacuation and resettlement; decontamination of land and buildings; restriction of access to severely contaminated areas; limitation of the consumption of contaminated food; and agricultural countermeasures. For some countermeasures, estimates of their cost-effectiveness are given. The prospects for the economic and social rehabilitation of contaminated areas are considered. Since the need for agricultural countermeasures will continue for a long time and economic rehabilitation will require considerable investment, it is crucial to inform the population about current and likely future radiological conditions. 1

10 1. INTRODUCTION 1.1. Background Over one decade after the Chernobyl accident, the levels of radioactive contamination 1 of the affected territories are generally well known. At the instigation of national and international organizations, pertinent scientific and technical studies have been undertaken in order to reach a better understanding of the circumstances of the accident, the behaviour of radioactive materials in different environmental media and the most efficient methods of decontamination. Radiation doses to the population have been, and continue to be, assessed. In 1995, taking into account the completed and ongoing studies by other organizations as well as the results of the International Chernobyl Project completed in 1991, the IAEA formulated, in co-operation with the Institut de protection et de sûreté nucléaire (IPSN) in France, a project focusing on the environmental impact of the Chernobyl accident in the Russian Federation, Belarus and Ukraine Objective and scope The project aimed to make the findings of the scientific studies comprehensible to and relevant for the decision makers who would form the target audience. Thus, the study focused on future environmental impact and was complementary to the other studies performed. It was a synthesis of available material and reports. The questions to be addressed within the scope of the project were, for example, whether or not people could live safely in the areas studied, whether or not agriculture could be resumed and, if not, how and when safe living conditions could be restored in those areas. The effects of the remedial actions taken and the development of criteria for these actions internationally and in the three republics were described. Issues related to the preservation of the natural environment were also addressed. The project concentrated on chronic exposure of the population, at the same time looking at particular areas, such as the exclusion zone, the Gomel region and part of the Bryansk region Structure The project addressed four different but interrelated issues. The four main sections of the report (Sections 2 5) describe the issues. Section 1 describes the situation as of 1996, and includes the mapping of deposited radioactive materials and quantification of the contamination, a prognosis of how and at what rate these levels will change in the future, and numerical estimates of the resulting exposure of the inhabitants, with and without countermeasures. Section 2 describes living conditions in selected areas, where high unemployment and a lack of capital investment, and also the actions taken to manage the situation, have been obstacles to industrial and agricultural development. 1 The word 'contamination' is used here to describe any level of artificially produced radionuclides, not associated necessarily with a 'hazard' to health. Any estimate of the potential detriment must be based on the actual level of contamination. 2

11 Section 3 reviews the effects on the natural environment in the more contaminated areas. Section 6 discusses possible remedial actions. The development, effects, cost and efficacy of such remedial actions as the resettlement of exposed people, the decontamination of urban sites, and the modification of forestry and agricultural practices are described in some detail. The general conclusions drawn from each section complete the report. Annex I defines the areas and zones discussed in the report. Annex II reviews the international criteria for long term countermeasures. 3

12 2. CURRENT RADIOLOGICAL SITUATION AND PROGNOSIS FOR THE FUTURE 2.1. Soil contamination with radionuclides Release of radionuclides and contamination of territories As a result of the accident to Unit 4 of the Chernobyl nuclear power plant (NPP), the environment was contaminated with radioactive materials whose total activity amounted to approximately 12.5 EBq (1 EBq = Bq), including 6.5 EBq of noble gases. This is the sum, as of 26 April 1986, of all the radionuclides with a half-life of more than one day. Table I presents the assessment by different authors of the release of specific radionuclides [1 4]. It should be noted that the most recent estimates (columns [3] and [4] of Table I) give significantly different figures from the initial ones (column [1] of Table I), especially for iodine and caesium releases. The quantities of iodine and caesium radioisotopes released represent 50 60% and 30 35% respectively of the core inventory of these nuclides at the time of the accident. Owing to the specific features of the accident (i.e. the long duration of the release of radioactive products into the atmosphere, the complex changes in physical and chemical makeup) and to the change in meteorological conditions, the local and distant contamination was non-uniform, not only in fallout density and radionuclide composition, but also in its physicochemical characteristics. An analysis of meteorological conditions during the period of the most intense release of radioactive products (26 April 5 May 1986) has made it possible to establish that the radionuclide contamination on the territory of the Ukrainian and Belarus Polessye (the 'western trace') was mainly due to the release which took place on 26 and 27 April. The contamination of the eastern regions of Belarus and of the European part of the Russian Federation (the 'northeastern trace') was due to the release which occurred between 27 and 29 April. Air mass transfer towards the south, which began on 30 April, was responsible for contamination in Ukraine, through both the release of radioactive products which took place between 30 April and 5 May, and the return of air masses from Belarus and the Russian Federation contaminated by earlier releases [5 7]. The radioactive fallout in the Russian Federation, in much of Belarus and in the Ukrainian Polessye contained a larger proportion of volatile nuclides such as 103/106 Ru, 131 I and 134/137 Cs and for these territories, the 90 Sr/ 137 Cs ratio varied within the range The contamination of the area of Ukraine south of the Chernobyl NPP contained non-volatile elements such as 95 Zr, 95 Nb, 141,144 Ce, and 140 La. The 90 Sr/ 137 Cs ratio varied in that area within the range The pattern of contamination was mosaic-like, with high gradients of radionuclide concentration, usually due to rainfall coincident with the passage of the plume. During the months immediately after the accident, the short-lived radionuclides were present mostly in soil deposition, among which 131 I had the greatest radiological significance. Figs 1 [5] and 2 [8] show the maps of 131 I deposition in Belarus and in part of the Russian Federation; these maps are deduced from comparison with 137 Cs deposition in the soil. The highest soil contamination by radioiodine has been estimated to exceed kbq m -2 [9]. 4

13 TABLE I. ASSESSMENT OF ACTIVITY OF RADIONUCLIDES RELEASED AS A RESULT OF THE CHERNOBYL ACCIDENT Nuclide Activity (PBq) [1]* [3]* [4]* 85 Kr Sr Sr Zr Mo Ru Ru m Te Te I Xe Cs Cs Ba Ce Ce Np Pu Pu Pu Pu Pu Cm Total * The numbers in square brackets refer to references. In the Russian Federation, the reconstruction of 131 I maps has been carried out by the statistical analysis of the results of gamma spectrometry of soil samples. Statistically significant regression relations between activities of 131 I and 137 Cs, depending on the distance between the point of the sample collection and the power plant, have been obtained for the northeastern trace [8]. In order to draw the 131 I deposition map in Belarus, the following data were used [5, 9]: direct gamma-spectrometry measurements of the 131 I content in soil samples for May July 1986; gamma-spectrometry data of the 131 I content in samples of daily depositions; correlation between the 131 I and 137 Cs content in soil; assessment of the 131 I contribution to the gamma radiation dose rate in May

14 At a later stage, the radiological impact was mostly due to 134 Cs and 137 Cs deposited on land. Maps of the 137 Cs contamination of the three republics are shown in Figs 3, 4 [7], and 5 [6]. Table II shows the areas of land within the different radioactive contamination zones defined in the legislation of these countries. TABLE II. AREA OF 137 CS CONTAMINATION OF THE TERRITORIES OF BELARUS, THE RUSSIAN FEDERATION AND UKRAINE AS OF 1 JANUARY 1995 (thousand km²) Country (1 5) 137 Cs soil deposition, kbq.m -2 (Ci.km -2 ) (5 15) (15 40) > 1480 (> 40) Belarus Russian Federation Ukraine Total By way of illustration, Fig. 6 and Fig. 7 show estimates of the levels of contamination in Belarus by 90 Sr and Pu respectively. On a large part of the State Polessye Radiological and Ecological Reserve, Pu surface activity exceeded 3.7 kbq.m -2. In the most contaminated regions of Russia, 90 Sr soil deposition varied from 0.4 to 70 kbq.m -2, corresponding to 1 5% of the 137 Cs fallout. Compared with the exclusion zone, lower levels of soil contamination with Pu were measured in southwestern parts of the Bryansk region (less than 0.7 kbq.m -2 ) and in the Tula and Kaluga regions (less than 0.3 kbq.m -2 ). In the Ukrainian exclusion zone, the level of soil deposition of 90 Sr in some areas exceeded 5000 kbq.m -2 and the soil deposition by Pu exceeded 100 kbq.m -2. In Ukraine, on about km 2 90 Sr contamination now exceeds 5 kbq.m -2 and on about 1000 km 2 it exceeds 111 kbq.m -2. After the evacuation of the population within the 30 km zone in April and early May 1986, the area closest to the reactor site (over 4000 km²) was excluded from cultivation. At present, this exclusion zone includes 2100 km² in Belarus (the Polessye Radiological and Ecological Reserve), 2040 km² in Ukraine (the Ukrainian exclusion zone) and 170 km² in the Russian Federation, which have the highest contamination levels. The deposition is largely characterized by 137 Cs, 90 Sr and the transuranium elements. About 95% of the radioactive contamination remains in the top 5 8 cm of the soil. The principal physicochemical forms of the fallout are dispersed fuel particles, condensation-generated particles and mixed-type particles, including adsorption-generated ones. The narrow, clearly outlined, fork-shaped western trace of radioactive contamination, whose width at a distance of 13 km from the damaged reactor does not exceed 1.5 km, is characterized by the predominance of fuel particles over the condensation-generated ones, and by high contamination levels; along the axis of the western trace, the levels of 137 Cs activity exceed kbq.m -2 [10]. The northern pattern of fallout is characterized by the fact that the contribution of the condensation-generated particles increases with distance from the reactor, until they become dominant at great distances from it. Text cont. on page 11. 6

15 Fig. 1. Map of 131 I soil deposition in Belarus, as restored for May 10, 1986 (kbq.m -2 ). 7

16 Fig. 2. Map of 131 I soil deposition in the West of the Russian Federation as restored for May 10, 1986 (kbq.m -2 ). Fig. 3. Map of 137 Cs soil deposition in Belarus, as restored for January 1st, 1995 (kbq.m -2 ). 8

17 Fig. 4. Map of 137 Cs soil deposition in Ukraine (kbq.m -2 ) [7]. 9

18 Fig. 5. Map of 137 Cs soil deposition in the west of the Russian Federation [6]. Fig. 6. Map of 90 Sr soil deposition in Belarus, as restored for January 1 st, 1995 (kbq.m -2 ). 10

19 Fig. 7. Map of Pu soil deposition in Belarus, as restored for January 1 st, 1995 (kbq.m -2 ). More than 70% of the exclusion zone is contaminated with over 500 kbq.m -2 of 137 Cs, over 100 kbq.m -2 of 90 Sr, and over 3 kbq.m -2 of 239/240 Pu. The deposition of radioactive material was most widespread in Belarus, where 23% of the land, populated by 2.2 million people (over one fifth of the total population of Belarus), has sustained radioactive contamination of over 37 kbq m -2 of 137 Cs. In Ukraine, the areas classified as radioactive contamination zones are inhabited by over 2.4 million people, and in the Russian Federation by 2.6 million people. Waste sites are mostly located in Ukrainian exclusion zone. According to recent assessments, the shelter contains about 180 tonnes of nuclear fuel with radioactivity exceeding 740 PBq (20 MCi) [11]. The 1996 National Report of Ukraine [12] states that this radioactivity includes 229 PBq (6.2 MCi) of Cs, 122 PBq (3.3 MCi) of Pu, 7.4 PBq (0.2 MCi) of 241 Am, 52 TBq (1.4 kci) of 14 C and 7.4 PBq (0.2 MCi) of 60 Co. The shelter also serves to store large quantities of radioactive products comprising the remains of the damaged reactor, such as graphite and other contaminated material. The radioactive waste burial sites, created during emergency and decontamination activities, and other temporary waste burial sites, contain radioactive products whose total activity amounts to 15 PBq and whose volume is approximately m 3 [12]. Eight hundred temporary radioactive waste burial sites for contaminated structures are distributed in the vicinity of the damaged reactor Vertical migration of radionuclides in the soil The rate of radionuclide migration in the soil-plant system is determined by a number of natural phenomena, including relief features, type of vegetation, structure and properties of the soil, hydrological and weather conditions, and physical and chemical characteristics of the 11

20 radionuclides and their isotope carriers in the soil [13 16]. Agricultural practices and other factors have an impact on radionuclide behaviour. Depending on the type of soil tillage and on the tools used, a mechanical redistribution of radionuclides in the soil may occur. The system of soil improvement measures which has been implemented also has an impact on the physicochemical state and on the mobility of radionuclides [14, 17 19]. The vertical migration of 90 Sr and 137 Cs in the soil of different types of natural meadows has been rather slow, and most of the radionuclides are still contained in its upper layer (0 10 cm). However, the type of vertical radionuclide migration depends on the type of meadow, its drainage and soil features. The 90 Sr and 137 Cs migration rates are significantly slower in dry meadows than in wetlands. In peaty soils, radionuclide migration is faster: eight years after the accident, the maximum radionuclide concentration was measured at a depth of 3 5 cm. In such soils, the characteristic radionuclide distribution is determined not only by their migration into deeper soil layers but also by the increasing amount of dead vegetable biomass in the upper layer of the soil. Chernobyl-originated 90 Sr and 137 Cs in peaty soils may be detected even at a depth of 20 cm. On average, in the case of peat soils, 40 70% of the 90 Sr and 137 Cs is found in the 0 5 cm layer; in the case of mineral soils, up to 90% of the 90 Sr and 137 Cs is found in this layer. Fig. 8 shows profiles of 90 Sr and 137 Cs vertical distribution in the Chernigov region which are typical for the soddy-podzolic soils prevailing in the contaminated territories of the polessye. The most important characteristics of soil which influence the migration of radionuclides are the mineral and physical composition of the soil, its organic composition, its cation exchange capacity and its acidity [13, 15, 16, 20]. Fig. 8. Depth distribution of 137 Cs and 90 Sr in undisturbed soddy-podzolic soils in the Chernigov region, Ukraine,